The present invention relates to a magnetic disk drive and more particularly concerns a management method for managing reproduction errors when it is required that data read from the disk drive should has continuity (in other words, it is required that more than a certain amount of data should be read within a specified time).
Conventionally, the disk drive executes a data reproduction process with top priority placed on the reliability of data. For this reason, if an error is detected during reproduction of data, retry of reproduction (hereafter referred to as retry) is repeated until no errors are detected or until a specified number of retries is reached. After this, an error correction process is carried out when necessary.
An example of the mode that places top priority on the continuity of data is the read continuous mode (hereafter referred to as “RC mode”) provided in the SCSI-3 (Small Computer System Interface-3) Standard of ANSI (American National Standards Institute). The RC mode is a mode in which data with a required length is transferred without performing a retry or error recovery and therefore, when an error occurs, erroneous data is transferred as it is.
As means for clarifying the content of the error, the above-mentioned SCSI-3 Standard provides the REQUEST SENSE command, by which the user can know the contents of errors and a LBA (Logical Block Address) where the error occurred.
There is technology for simultaneously outputting data and error information to a host system, one example of which is disclosed in JP-A-07-320418. According to this prior art, separate transfer lines are provided for data and error information, through which data and error information are output at the same time.
In reproduction with most preference on reliability of data, when an error is found in reproduced data, extra time is taken for retry (including rotational delay time) and error correction than when no error is found. As this excess time is consumed, an amount of data to be processed within a specified length of time cannot be processed in time, so data being deprived of its continuity.
When data is reproduced in the RC mode that gives top priority to data continuity, if reproduced data includes an error, this erroneous data is transferred without notifying the error to the host system, such as a host computer. Therefore, the host system handles wrong data as correct data.
On the other hand, when the REQUEST SENSE command is used, if data transferred by one READ command includes a number of errors, only one piece of information error (LBA) is sent to the host system but the other errors are not notified to the host system. In addition, extra time is consumed, such as time for issuing a REQUEST SENSE command, data is likely to be deprived of its continuity.